The present inventions relates to railroad freight cars, and particularly to a well car of light-weight construction, for optionally carrying either intermodal cargo containers stacked one upon another or over-the-highway trailers supported on their own running gear in the well.
Railroad cars for carrying over-the-highway trailers are well known, as are railroad freight cars defining container wells for carrying various combinations of intermodal cargo containers stacked one upon another in two tiers. Because the total weight which can be carried upon the rails limits the net amount of cargo which can be carried on a railroad freight car, it is desirable for a well car to be constructed in a configuration having a minimum tare weight consistent with the strength required to safely support a combination of cargo containers for which the car is configured. It is also necessary, however, to provide an adequate surface to support the tires of trailers carried in the cargo well. Additionally, it is necessary for a car to be strong enough to withstand the many forces resulting from movement of the laden car as part of a train.
It is desired, then, to provide a well car having a floor defining an area sufficiently large and strong to support the wheels of laden trailers and also capable of carrying the concentrated stresses resulting from carriage of intermodal cargo containers, while still having a minimum tare weight.
It is also desirable to provide a well floor structure whose vertical height, or overall thickness, is kept small, in order to minimize overall height of the well car when it is laden with containers stacked atop one another.
It is also necessary to provide a shallow well depth from floor top surface to the top of side sill giving trailer loading equipment access to the bottom of a trailer floor above the side sills so that trailers can be inserted into and extracted from the well. The reduction of bending resistance resulting from shallower side sills must be restored by other structure.
In the past, well floor structures of satisfactory rigidity to support trailers have been more massive and greater in vertical thickness than is desired for well floor structures in a car intended to carry intermodal cargo containers stacked in two tiers, where the height of the center of gravity and the overall height of such a car when laden are of concern.
One of the particular problems encountered in the past in attempting to design a well car with a light, thin, and yet stiff and strong well floor has been the question of how to provide adequate strength in the areas of interconnection of such a well floor with the structure of the sides and end portions of such a car.
Previous attempts to provide the dual capacity for carrying containers or trailers have included cars incorporating transverse beams supporting substantial gratings on which to receive the tires of a trailer carried in the well, as disclosed in Pavlick U.S. Pat. No. 4,456,413. While such cars provide ample strength for carrying both containers and trailers, the structure is undesirably heavy, and the well floor thickness is greater than desired, leaving less than the desired amount of vertical space available for stacked cargo containers. The car disclosed in Gutridge U.S. Pat. No. 3,357,371 has a similar lack of vertical clearance.
Jamrozy U.S. Pat. No. 4,949,646, and Lindauer et al. U.S. Pat. Nos. 4,876,968 and 4,771,706 all disclose a well car for carrying containers, in which a well floor structure includes transverse floor beams. Johnstone et al. U.S. Pat. No. 4,782,762 discloses a well car including a floor with longitudinal and transverse beams, for carrying containers. Cordani U.S. Pat. No. 4,091,742 discloses a well car including a floor structure of transverse and diagonal beams for supporting containers, but none of these patents discloses structure for supporting the wheels of a trailer carried in such a well.
Jamrozy et al. U.S. Pat. Nos. 4,889,055 and 4,862,810 disclose a well car including longitudinal channels, transverse channels, and a longitudinal center plate in a well floor structure, but there is no disclosure of structure available to support the wheels of a trailer in the container well.
Hill U.S. Pat. No. 4,703,699 discloses a lightweight side sill structure for a well car for carrying stacked containers, in which an opening is provided in one of a pair of parallel sheets of material, and a stiffener ring surrounding the opening connects the margins of the opening with the other of the two parallel sheets of material.
Other cars, such as those operated by Canadian National Railroad as its CN679500 "Improved Laser" series cars include heavy gratings supported on the flanges of hat-shaped transverse beams, providing structure of ample strength but greater than desired well floor thickness and weight.
What is needed, then, is an improved structure for a railroad well car body for optionally carrying either stacked containers or trailers, in which a well floor structure and the connection of such a well floor to other parts of the car provide adequate strength without unnecessary weight and with shallow well depth and small floor thickness.